Electrical stimulation of nerves and surrounding tissue is used to treat a variety of conditions. For example, electrical stimulation can be used to restore partial function to limbs or organs following traumatic injury. Electrical stimulation can also be used to reduce pain. Specifically, electrical stimulation can be used to treat disorders associated with the gastrointestinal (GI) system, such as, obesity and gastroesophageal reflux disease (GERD).
Obesity is a common condition and a major public health problem in developed nations including the United States of America. As of 2009, more than two thirds of American adults, approximately 127 million people, were either overweight or obese. Data suggest that 300,000 Americans die prematurely from obesity-related complications each year. Many children in the United States are also either overweight or obese. Hence, the overall number of overweight Americans is expected to rise in the future. It has been estimated that obesity costs the United States approximately $100 billion annually in direct and indirect health care expenses and in lost productivity. This trend is also apparent in many other developed countries.
For adults, the body mass index (BMI) is used to determine if one is overweight or obese. A person's BMI is calculated by multiplying body weight in pounds by 703 and then dividing the total by height in inches squared. A person's BMI is expressed as kilograms per meter squared. An adult is considered overweight if his or her BMI is between 25 and 30 kg/m2. Obesity is defined as possessing a BMI between 30 and 40 kg/m2. A BMI greater than 30 kg/m2 is associated with significant co-morbidities. Morbid obesity is defined as possessing either a body weight more than 100 pounds greater than ideal or a body mass index (BMI) greater than 40 kg/m2. Approximately 5% of the U.S. population meets at least one of the criteria for morbid obesity. Morbid obesity is associated with many diseases and disorders including, for example: diabetes; hypertension; heart attacks; strokes; dyslipidemia; sleep apnea; pickwickian syndrome; asthma; lower back and disc disease; weight-bearing osteoarthritis of the hips, knees, ankles and feet; thrombophlebitis and pulmonary emboli; intertriginous dermatitis; urinary stress incontinence; gastroesophageal reflux disease (GERD); gallstones; and, sclerosis and carcinoma of the liver. In women, infertility, cancer of the uterus, and cancer of the breast are also associated with morbid obesity. Taken together, the diseases associated with morbid obesity markedly reduce the odds of attaining an average lifespan. The sequelae raise annual mortality in affected people by a factor of 10 or more.
Gastro-esophageal reflux disease (GERD) is another common health problem and is expensive to manage in both primary and secondary care settings. This condition results from exposure of esophageal mucosa to gastric acid as the acid refluxes from the stomach into the esophagus. The acid damages the esophageal mucosa resulting in heartburn, ulcers, bleeding, and scarring, and long term complications such as Barrett's esophagus (pre-cancerous esophageal lining) and adeno-cancer of the esophagus.
Gastric electrical stimulation (GES) is aimed at treating both obesity and GERD. GES employs an implantable, pacemaker-like device to deliver low-level electrical stimulation to the gastrointestinal tract. For obesity, GES operates by disrupting the motility cycle and/or stimulating the enteric nervous system, thereby increasing the duration of satiety experienced by the patient. The procedure involves the surgeon suturing electrical leads to the outer lining of the stomach wall. The leads are then connected to the device, which is implanted just under the skin in the abdomen. Using an external programmer that communicates with the device, the surgeon establishes the level of electrical stimulation appropriate for the patient. The Abiliti® implantable gastric stimulation device, manufactured by IntraPace, is currently available in Europe for treatment of obesity.
In another example, Medtronic offers for sale and use the Enterra™ Therapy, which is indicated for the treatment of chronic nausea and vomiting associated with gastroparesis when conventional drug therapies are not effective. The Enterra™ Therapy uses mild electrical pulses to stimulate the stomach. According to Medtronic, this electrical stimulation helps control the symptoms associated with gastroparesis, including nausea and vomiting.
Electrical stimulation has also been suggested for use in the treatment of GERD, wherein the stimulation is supplied to the lower esophageal sphincter (LES). For example, in U.S. Pat. No. 6,901,295, assigned to Endostim, Inc., “A method and apparatus for electrical stimulation of the lower esophageal sphincter (LES) is provided. Electrode sets are placed in the esophagus in an arrangement that induce contractions of the LES by electrical stimulation of the surrounding tissue and nerves. The electrical stimulus is applied by a pulse generator for periods of varying duration and varying frequency so as to produce the desired contractions. The treatment may be short-term or may continue throughout the life of the patient in order to achieve the desired therapeutic effect. The stimulating electrode sets can be used either alone or in conjunction with electrodes that sense esophageal peristalsis. The electrode sets can be placed endoscopically, surgically or radiologically.” The referenced invention relies on sensing certain physiological changes in the esophagus, such as changes in esophageal pH, to detect acid reflux. Once a change in esophageal pH is recognized, the system generates an electrical stimulation in an attempt to instantaneously close the LES and abort the episode of acid reflux. U.S. Pat. No. 6,901,295 is hereby incorporated by reference in its entirety.
The leads used in electrical stimulation of gastrointestinal tissues traditionally comprise elongated or coiled, insulated wires or cables having a means for attachment to an electrical pulse generator at one end and one or more exposed electrodes at the other end. The leads are typically anchored in place such that the electrodes are positioned and remain proximate the target nerve or tissues. Anchoring is often accomplished by suturing the electrode containing ends of the leads proximal to the electrodes and into the surrounding tissue. Traditional leads often comprise a needle attached to a length of suture nylon at the distal end of each branch of the lead. A butterfly shaped anchoring element is positioned on each branch just proximal to each electrode. The needle and suture nylon are used to create a pathway for the electrode to be inserted into the tissue, with the needle and most of the suture being removed thereafter. The remaining suture is used as a tether onto which at least one clip (e.g., titanium clip) is used to provide a distal stop thus preventing the electrode from backing out until sufficient fibrosis is formed.
While current electrical leads are effective in transmitting electrical stimulation to target nerves and tissues, they are not without their drawbacks. For example, the overall length of current leads limits the implantation site of the stimulator to which they connect. A lead that is intended to have its electrodes positioned proximate the gastroesophageal junction is often implanted through the abdominal wall via laparoscopy, but requiring the stimulator and its unsightly scar at the patient's exposed abdomen. Therefore, what is needed is a lead having an increased overall length to permit stimulator implantation at points further from the therapy site, whereby the scar could be covered by most clothing apparel (e.g., male and female swimsuits) or the implant access could be through the umbilicus.
In addition, with regard to bipolar leads, the monopolar branches that extend beyond the bifurcation point are often too long. Lengthy monopolar branches can become entangled in surrounding tissues, leading to dislodgment of anchored leads and stricture formation. Therefore, what is needed is a bipolar lead having shortened monopolar branches. Further, traditional leads are often pulled backward to facilitate anchoring, causing the proximal 2 to 3 mm of conductive material to become exposed. Exposed conductive material can result in inadvertent electrical stimulation of non-target tissues as well as less stimulation current reaching the target tissues. Therefore, what is also needed is a lead having additional insulation closer to the electrodes.
Traditional leads also include electrodes that are too large for certain applications, including stimulation of the gastroesophageal junction. Oversized electrodes can also result in inadvertent electrical stimulation of non-target tissues. Therefore, what is needed is a lead having smaller sized electrodes. In addition, the space in which to work surrounding the gastroesophageal junction (GEJ) is relatively confined compared to other spaces, such as, around the body of the stomach. Traditional leads having long suture nylons tempt the surgeon to use the same needle and suture for anchoring the lead proximal to the electrode; however, this suture material is chosen for applying distal clips and not anchoring the leads. Therefore, what is also needed is a lead having shorter suture nylons on each branch such that this needle and suture is not long enough to be used for anchoring the leads proximal to the electrode. Having shorter suture nylons also reduces the number of pulling maneuvers required in order to bring the electrode(s) into final position. Traditional leads often include a curved needle for anchoring. The degree of curvature of the needle is often not sufficient when considering the adjacent tissues, resulting in injury to the tissue. What is needed is a needle curvature which will allow the user to significantly bury the electrode within the target tissue while also making the needle easily retrievable from the tissue exit site without puncturing or scraping nearby tissues.
Therefore, what is needed specifically for GEJ implantation is a lead having a needle with a degree of curvature specific to the target and surrounding tissue. Some traditional leads include an additional suture sleeve over the lead body to prevent damage to surrounding tissues during implantation. However, this sleeve tends to attract much fibrosis. Therefore, what is also needed is a lead having no additional anchoring sleeve.
Traditional leads are often implanted laparoscopically via an incision site on the abdomen. The incision typically leaves several visible scars and use of anchoring needles usually results in some trauma to the internal tissues. Applying suture anchors through an endoscope are difficult, specifically in the confined space of the GEJ or in a small endoscopic tunnel. Therefore, there is also a need for an electrical lead that can be implanted using an endoscope and can be anchored to surrounding tissues without using needles and sutures.